Manufacture of malleable cast iron



Patented 28,1928. 4

UNITE STATES PATENT orrlca.

HARRY a scnwaa'rayor cnnvnnaun smears, omo, ASSIGNOR r inrrouan m LEAIBLE AND s'rnnn cas'rmes COMPANY, or onnvnnann, 0510, A. eoarona'rron' manurac'rnnn or uannaaisnn casr men. I

No Drawing.

My invention relates-to the manufacture of malleable cast iron, and particularly to the overcoming of graphitization difliculties normally met within the annealing operation in such manufacture.

It is well known that elements such as sulphur, selenium and tellurium, which form v readily non-metallic compounds with iron,

are a detriment to annealing. This is usually attributed (as when sulphur is present) to the formation of films or networks of sulphides about the iron and iron-carbon crystals which hinder the migration ofcarbon during annealing. In practice this diliiculty is usually overcome by adding suflicient 'manganese, which readily combines with the sul-.

. manganese, a rare earth phur to form globules of manganese sulphide instead of iron sulphide films. If, however, too great an excess of manganese is added, this also interferes with annealin and where the percent of sulphur is varia le andnot known in advance there is danger of having a harmful excess of manganese whenthe su1-' phur is less than is anticipated.

I have found, 'however' that if, instead of element such as cerium is added, just before pouring the molten metal in a quantit in the ratio of not harmful in annealing it is not a mat-.

ter of importance, except forthe sake of economy, whether the excess is large or not.

Normally the cerium addition is approximately 25% to .50% and is added preferably in the form of Misch metal just before the metal is tapped, or in the ladle. As substantially all of the sulphur readily combines with the cerium, the manganese is left free to alloy'with the metal itself. Hence, by the useof cerium the eflects of sulphur, selenium and tellurium on graphitization may be completely controlled without the neeessity of carefully regulatin the controlling actor, as is the case wit manganese.

phur has been taken u Application filed October 22,1026. Serial No. 14am A typical iron used for makin "malleable iron contains carbon 2.50%, si con .80%,

manganese 26%, sulphur '.07%, phosphorus.

18%. If the sulphur is to be counteracted by cerium 1t 1s not necessary to have such high manganese, and the amount of manganese would be controlled to avoid interference with annealing by that element.

I have found also that so'far as tin is-ooncerned, as the sul hur combines with the cerlum more readi y than it does with tin, the harmful eifect of the tin sulphide, which 1s more pronounced than iron sul hide, is prevented, and the tin,-'since all 0 the'sulp by the cerium as cerium sulphide, will,'li e the manganese in small excess, combine with their-on in such a.

way as not to impair the qualities of the iron. v v

I have observed that where iron sulphide forms in the making of malleable iron, as .its

melting point is lower than that of the bulk of the mass, it solidifies after the iron and iron-carbon compounds and thus has the opportunity of forming a network or series of films around the already formed iron and iron-carbon crystals which seriously retards' graphitization during annealing, as such network or series of films interfereswith the separation of the carbon from the mass in the form of temper carbon.-

I have also observed that normall a rare earth metal such as cerium will combine with the sulphur to form acompound the melting po nt ofwhich is above that of the mass as a,

whole, and when the mass. cools this compound will freeze out of the mass as globules or included grains which will not hinder graphitization, as where iron sulphide forms.'

In other words, a rare earth metal, asit has a greater aflinity for sulphur than does iron, and as its sulphide has a higher melting point than the ulk of the molten mass, solidifies while the rest of the mass isliquid and .is-thus free to form the globules or included grains which in the subsequent annealin operation do not hinder the separation 0 the carbon from the iron-carbon compounds.

It will thus be seen that by the used cerium, which does not have to be regulated in amount as does man ane e because an excess has no harmful efl ect, I .have provided an element which very efl'ectively renders in- -nocuous such metalloids as sulphur, seleadded element must have a greater aliinity for the harmful metalloid (as sulphur) than has the otherelement (as iron) of the original compound; that the melting point of its compound with the metalloid should be higher than that of the bulk of the mass; and that it is desirable that its presence in excess over that required to combine with the metalloid be not harmful to graphitization.

The terms and expressions which I=have employed are used as terms of description an not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described, or portions thereof, but recognize that various modifica-- metalloid is not armful to tions are possible within the scope of the invention claimed.

What I claim is; v

1. That improvement in theart of making malleable iron castings which comprises melting the iron", adding to the molten iron a rare earth element having a greater alfinity for a metalloid contained in the molten iron, such assulphur, than it has for the iron, cast ing the metal, whereby as the mass cools the element combined with the metalloid freezes out of the mass in the form of included globules at a higher temperature than the freezing point of the bulk of the mass, and in whic the presence of the element in excess of the amount re wired to combine with the aphitization.

2. That improvement in t e art of making malleable iron castings which comprises melting the iron, adding to the molten iron an element of the carium group havin a greater aflinity for a metalloid contain in the molten iron, such as sulphur, than it has for the iron, casting the metal, whereby as the mass cools the element combined with the metalloid freezes out of the mass in the form of included lobules at a hiher temperature than the reezing point 0 the bulk of the mass, and then the mass freezes at a lower temperature, whereby the combined carbon is free to separate out of the mass during the subsequent annealing operation, the presence of the element in excess of the amount required to combine with the metalloid not being harmful to graphitization. a

3. That improvement in the art of making malleable iron castings which comprises melting the iron, adding to the molten iron an element of the cerium group, casting the metal, whereby as the mass cools the element combined with a metalloid iron freezes out of the same in the form of included globules at a hi her temperature than the freezing point 0 the bulk of the mass and in which the presence of the ele-' ment in excess of the amount required to combine with the metalloid is not harmful to graphitization.

4. That improvement in the art of making malleable iron castings which comprises meltin the iron containing metalloids such as sulp iur, adding cerium to the molten iron and casting the metal, whereby as the mass cools the cerium combined with the sulphur first freeze out of the mass as cerium sulphide in the form of included globules and then the mass as a whole freezes, thereby render ing the combined carbon in the mass free to separate out as temper carbon in the subsequent annealing operation.

5. That improvement in the art of making malleable iron castings which comprises melting the iron containingelements having an affinity for each other such as tin and sulsulphur than it has for the tin or the iron,

and casting the metal, whereby as the mass cools the added element combined with the sulphur freezes out of the mass and the formation of sulphide of tin is thus avoided.

' HARRY A. SCHWARTZ. 

